Anesthesia delivery system

ABSTRACT

An improved anesthesia delivery system in which carbon dioxide laden gases expirated by a patient are passed through a material which reacts with carbon dioxide exothermically. The material, which may be granular, surrounds a water-filled canister containing a gas diffusion stone into which anesthetic laden gas is fed and from which humidified anesthetic laden gas is removed. The heat produced aids in the humidification of the inspired gas.

United States Patent 91 Chalon Dec. 2, 1975 ANESTI-IESIA DELIVERY SYSTEM [75] Inventor: Jack Chalon, Tarrytown, NY.

[73] Assignee: Albert Einstein College of Medicine-Division of Yeshiva University, New York, NY.

[22] Filed: June 20, 1974 [21] Appl. No.1 481,167

[52] US. Cl. 128/188; 128/193; 128/212; 126/263; 23/288 F [51] Int. Cl. A61M 16/00 [58] Field of Search ..128/l88,186,191R,193, 128/194, 142, 212; 261/77; 126/263; 239/129; 23/288 F [56] References Cited UNITED STATES PATENTS 1,094,301 4/1914 Caine 128/188 2,549,593 4/1951 Gardenier 128/188 FOREIGN PATENTS OR APPLICATIONS 1,303,047 7/1962 France 128/188 HYGROMETER INDICATOR' OTHER PUBLICATIONS J. Chalon et a], Water Nebulization in a Non- Rebreathing System during Anesthesia, Nov. 1973.

J. Chalon et a1, Humidity Output of the Circle Absorber System, May, 1973.

Primary ExaminerRichard A. Gaudet Assistant Examiner-Henry J. Recla Attorney, Agent, or Firm-Bierman & Bierman [57] ABSTRACT An improved anesthesia deli-very system in which carbon dioxide laden gases expirated by a patient are passed through a material which'reacts with carbon dioxide exothermically.

The material, which may be granular, surrounds a water-filled canister containing a gas diffusion stone into which anesthetic laden gas is fed and from which humidified anesthetic laden gas is removed. The heat produced aids in the humidiflcation of the inspired gas.

13 Claims, 4 Drawing Figures llll UQSQPatent Dec. 2,1975 Sheet 1 of2 3,9

FlYGROMETER INDICATOR PATIENT US. Patent Dec. 2, 1975 Sheet 2 on 3,923,057

IOO

E (I O LL] 0: D 40 MIN. VAP. PRESS. m O: O.

o l l l I l l l l l l 2 3 4 5 6 7 8 9 IO FLOW (Liters/min) F/GZ ANESTI-IESIA DELIVERY SYSTEM This invention relates to anesthetic delivery systems and more particularly to gaseous anesthetic delivery in which the gas is humidified prior to inspiration by the patient.

It is known that inspiration of dry anesthetic gases can lead to damage of the ciliated columnar epithelial cells of the tracheobronchial tree. The effects of dry anesthetic gases are more fully discussed in the article entitled Humidity Output of the Circle Absorber Systern by J. Chalon et al., Anesthesiology Volume 38, No. 5, May 1973. In accordance with the teaching of this article, a significant cellular change can be avoided if the gas is properly humidified. Best results are obtained when the gas is humidified to 60% at room temperature (2226C) or saturated with moisture at body temperature.

One of the drawbacks of prior art anesthesia delivery systems, and in particular the device commonly known as the Circle system, is that supplemental humidification of the anesthetic gas is achieved by the delivery of power, usually electrically generated heat. Since anesthetic gases are highly explosive, the use of electricity or any other type of flame or spark producing means can be extremely dangerous. Safety controls must be used which significantly increase the cost of the delivery system without totally eliminating the explosion hazard.

Some anesthesia systems are humidified by nebulizers which emit water droplets instead of water vapor. The disadvantage inherent in humidifying with water droplets is that with improper sterilization these droplets may become laden with bacteria, a factor that does not obtain when water vapor is used. In addition nebu- ,lizers may emit large amounts of water which may be harmful to the patient, whereas vaporizers are limited in their water output by the temperature at which they operate (about 29C) for anesthesia delivery systems. Furthermore, water droplets are heavy and either settle or get trapped, via some mechanism, in the air passages before reaching the gas exchange surface of the alveoli which are in most need of protection from desiccation. These trapped droplets may block some of the microscopic air passages, thus interfering with efficient respiration. These problems do not arise when water vapor is used.

The more common system of anesthesia delivery utilizes an absorbent granule filled canister, such as lime,

with or without a separate humidifier. However, the moisture output of the humidifier will in and of itself decrease with time because vaporization will cool the water in the humidifier. It is to obviate the undesired decrease in vapor output from the humidifier which has in the past dictated the use of electrically heated and thermostatically controlled humidifiers, even though an explosion hazard w'as concurrently introduced into the system.

In accordance with the present invention, a material which reacts with carbon dioxide in an exothermic reaction and the humidification apparatus are placed in a canister with the reactive material surrounding the humidification section of the apparatus. Carbon dioxide containing gases are introduced into the reactive material to react therewith. Carbon dioxide is neutralized by the reaction and heat is released. The heat of reaction is used to heat water contained in the humidification section into which dry anesthetic gas is introduced. The dry gas picks up humidity and is then fed through an inspiration tube to the patient. As can be readily appreciated, heat for vaporization is generated without the use of outside power sources and the danger of explosion is eliminated. The carbon dioxide laden gases may come from the gases expirated by the patient or from a separate source if desired.

The reactive material may be a material or mixtures thereof which react with carbon dioxide in an exothermic reaction. Preferably, the oxides or hydroxides of the alkaline earth metals and alkaline metals of Groups I and II of the Periodic Table are used, such as CaO, Ca(OH) Li O, LiOH, Ba 0, Ba(OH) Sr O, SrOH, MgO, Mg(OH) A1 0 Al(OH) La O La(OH) FeO, NaOH, KOH. Guanidine or substituted guanidines in which the pK value is more than 10 are also useful and it is even possible to use strongly basic anion exchange resins which retain their positive charge up to pH 12. Examples of such resins include trimethyl benzyl ammonium and dimethyl ethanol benzyl ammonium ion exchange resins. The last two mentioned resins are products of Dow Chemical Company and sold under the trademarks Dowex 1 and Dowex 2 respectively. In addition, diethanol amino ethyl cellulose (DEAE cellulose), epichlorhydrin triethanolamine cellulose, DEAE Dextran, polyethylene imine cellulose and triethyl aminoethyl cellulose are suitable. Mixtures of the foregoing can be blended to achieve the desired CO absorption and heat generation characteristics.

The most preferred reactive materials are the oxides and/or hydroxides of calcium, barium or lithium. For best results, the reactive material is in granular, powdered, or open cellular form to permit passage of carbon dioxide laden gases into and through the reactive material.

In accordance with another aspect of the instant invention, a bypass valve is provided between the humiditied output line and the dry gas input line. By opening and closing the by-pass valve, the humidity level can be controlled by simply adding dry gas to the humidified gas. It has been found that inspired humidity can be regulated quite accurately from about 8 mg H O/liter of gas to about 23 mg H O/liter of gas (40 to 116% relative humidity at 23C).

Referring now to the drawings in which like numerals refer to like parts:

FIG. 1 is a schematic diagram of an anesthesia delivery system in accordance with the present invention;

FIG. 2 is a graph depicting the relationship of pressure in the vaporizer as a function of gas flow in liters per minute;

FIG. 3 is a graph depicting the relationship of inspired humidity at the patients mouth with time;

FIG. 4 is a plan view of a streamlined vaporizer useful in the system of FIG. 1.

The anesthesia delivery apparatus as shown in FIG. 1 basically comprises a conventional anesthesia machine 10 through which dry anesthetic gas is fed into the system. The anesthesia machine 10 is quite well known and in and of itself forms no part of the instant invention. As in generally all conventional anesthesia machines, gas flow can be controlled to any desired setting useful for live patients.

The output of anesthesia machine 10 is fed through tube 12 into a canister 14. Canister 14 contains a conventional gas diffusion stone 16 to which tube 12 is connected. Surrounding gas diffusion stone 16 is a pool of water 18.

Dry anesthetic gas, which generally contains oxygen, is put through anesthesia machine and travels through tube 12 to gas diffusion stone 16. The dry gas bubblesoutwardly from the gas diffusion stone picking up moisture at a rate dependent on the temperature of the water and of the gas. The moisture laden gas flows to the top of canister 14 and is removed through tube 20. Both tubes 12 and enter canister 14 through a second larger canister 22. Two ports 24, 26 are provided in canister 22 to allow tubes 20 and 12, respectively, to pass through to the canister 14.

Tube 20 is connected to a dome valve 28. The output 30 of dome valve 28 is connected to an inspiration tube 32 which terminates in a Y-connection 34. The single leg of the Y-connection is adapted for insertion into the patients mouth in conventional manner.

Moisture laden anesthetic gas is delivered to the patient through tube 32. Upon expiration, the carbon dioxide laden gases produced by the patient are exhaled into the Y-connection 34 and flow into expiration tube 36. Expiration tube 36 is connected to the input of an expiration dome valve 38 whose output is in turn connected to the upper portion of canister 22.

Canister 22 is filled with a reactive material 40 which reacts with carbon dioxide in an exothermic reaction. For best results, the reactive material is in granular, powdered or open cellular form to provide large surface area for the efficient removal of carbon dioxide. The most preferred reactive material is a barium hydroxide-lime granulated mixture of U.S.P. grade.

The carbon dioxide laden expirate travels downwardly through the reactive granular material 40 and at least some of the carbon dioxide reacts therewith to produce heat and some water. The type and amount of reactive material is chosen so that when the carbon di oxide is entrained in gases expired by a patient, sufficient carbon dioxide will be removed via said reaction to permit the remaining expirate to be sent back to the patient, along with humidified gases containing dry anesthetic and preferably oxygen, in a closed system. For best results an excess of reactive material is placed in the canister 22 to permit absorption of carbon dioxide as breathing rates increase and to permit the continuous use of the reactive material over a long period of time.

An outlet chamber 42 is provided at the bottom of canister 22. The outlet chamber is connected to a return duct 44 which is connected at its extreme end to inspirational dome valve 28. Carbon dioxide cleansed gases are thus recirculated to the dome valve 28 and mixed with fresh moisture laden anesthetic gas for return to the patient along inspiration tube 32.

About midway along return duct 44, a branch duct 46 is provided which in turn is connected to a conventional anesthetic bag or ventilator 48. A conventional pop-off valve 50 may be provided as a safety measure.

As described above, the neutralization of carbon dioxide by reaction with the reactive material produces heat. The heat so produced warms the water 18 and helps prevent the vaporizing action from decreasing over a period of time as will tend to occur in other systems. The amount of heating produced to warm the water in the present invention is proportional to the amount of carbon dioxide reacted with the reactive material 40. As can be readily appreciated, not only can the use of externally applied energy sources for heating the water be dispensed with along with the omnipresent risk of explosion, but the amount of heat produced in the reaction increases as breathing increases since the rate of carbon dioxide input to the reactive material also increases. The apparatus of the present invention is therefore self regulating to an extent not generally achieved by the prior art. Of course, a separate carbon dioxide supply can be used to react with the absorbent granules in the event a nonrebreathing type of apparatus is used.

Quite often condensate will collect in tube 20. This condensate can be removed through short tube 49. A standard clamp 51 is shown which normally pinches tube 49 to prevent gas leakage out through tube 49. When it is desired to drain condensate, clamp 51 is opened and left open until the condensate is drained.

In order to retain full control over humidity levels, tube 20 is placed in fluid communication with inlet tube 12 through bypass tube 53. A bypass valve 55 is provided in tube 53, such as a conventional clamp. The valve 55 is maintained in a normally closed condition when humidity in tube 20 or at the Y-connection 34 is at a selected level. If less humidity is desired, bypass valve 55 is opened to permit dry anesthetic gas to enter tube 20 directly to mix with and reduce the relative humidity of the anesthetic gas flowing to dome valve 28 from canister 14.

FIG. 4 depicts another embodiment of the first or inner canister 14. It has been found during tests that a rectangular container of the type shown in FIG. 1 leaves a conical area of reactive granules both above and below the canister in an unreacted state. The more streamlined canister 52 shown in FIG. 4 has the gas diffusion stone 16 positioned at the bottom thereof. Tube 12 inputs directly underneath gas diffusion stone 16 through opening 54. Water 18 covers the diffusion stone and outlet tube 20 is positioned at the top of the canister.

Of course, all connections shown in the drawings are preferably made airtight to prevent any leaks from occurring within the system. An acrylic cement can be used if desired to achieve the aforesaid airtight connections.

The apparatus shown in FIG. 1 is instrumented for test purposes and also for humidity control during use. An aneroid manometer 56 is connected to tube 12 to measure the pressure of anesthetic gas delivered to canister 14. A thermistor probe 58 is placed at the bottom of canister 14 and is connected to a conventional telethermometer for constant temperature readings of the water 18 and connected to a conventional readout 59. A conventional hygrosensor 60 is connected to the inspiration tube 32 just upstream of the Y-connection 34. The hygrosensor 60 is in turn connected to a conventional electric hygrometer indicator 62 which continuously indicates humidity of inspirational air at the Y-connection 34. A conventional thermometer 64 is also connected in the inspiration air stream to measure its temperature.

Three studies were conducted with the apparatus shown in FIG. 1 using a mixture of barium hydroxide and lime granules as the reactive material. The first, a laboratory study, substituted a 5 liter anesthesia bag for the patient. The bag was connected to the single leg of the Y-connection 34. A source of carbon dioxide having a calibrated meter was also connected to the single leg of the Y-connection. The system is described more fully in Humidity Output of the Circle Absorber System cited above. The system represents a model patient as discussed in said article. All temperatures, ineluding ambient temperature, were monitored at minute intervals and humidity recorded simultaneously. The thermostat of the humidifier was regulated to keep outlet temperature at 37C.

Absolute humidity in the inspiratory tube at the Y piece (mg H O per liter of gas) was studied with the bypass 55 closed and with a fresh gas inflow from the anesthesia machine 10 of 5 liters/min. Three experiments were conducted in the first study in which the volume of CO (V CO and ventilatory settings for the model patient were varied as follows:

1. Standard adult experiment: V CO 200 ml/min.

V, 600 ml. n=12.

2. Large adult experiment: as above but V CO 300 ml/min.

3. Pediatric experiment: V CO, 100 ml/min. V, 200 ml. "=20. Where v co is the carbon dioxide minute volume, V, is the total tidal volume of anesthetic gas and n is the number of breaths per minute.

In addition a fourth experiment was conducted to assess the degree of controllability of the humidity of the system. This was done by keeping the humidity reading on the hygrometer at 60% at ambient temperature (22-26C by adjusting the bypass clamp 55 and regulating the anesthesia machine input.

Presence of carbon dioxide in the inspiratory limb was tested with a Severinghaus Electrode after 5 hours of use with large adult settings.

The pattern of neutralization of the reactive granules in the canister was examined after each experiment.

The second study, a clinical study, was performed on 6 adult patients (four males and two females, aged 35 to 70 years of age and weighing between 42 and 72 Kgm). The patients were undergoing general endotracheal anesthesia for surgery during which the humidity and temperature of gases in the inspiratory tube at the Y piece 34 were recorded at 10 minute intervals.

Pressure variations in the inspiratory and expiratory tubes 32 and 36 were measured during all laboratory and clinical tests both with the canister 14 in the canister 22 and without it. The unit was also tested with the canister 14 in the unit to obtain a subjective feeling of resistance to breathing. Results for the six patients were generally the same as for the model patients. Only one is set forth in this specification and follows hereinbelow. PATIENT P.R. Male, aged 39 years. Weight 72Kg. Height 1.73 M. Operated on 11/16/73. Vagotomy and gastrectomy. Duration of anesthesia 4 hours. (Pentothal, succinylcholine, nitrous oxide in oxygen, and curare). Ventilation 600 ml X l2/minute. Mean room temperature 255C.

The patient was placed on a Foregger circle absorber system containing a humidifier in the absorber canister with the bypass closed off. Relative humidity and temperature of inspired gases was measured at the Y piece in the inspiratory limb. Absolute humidity was then calculated in function of humidity and temperature. All measurements were made at the onset of anesthesia and at ten minute intervals thereafter. At a room temperature of 25.5C absolute saturated humidity is 24 mg/liter.

At the onset of the procedure the absolute humidity in the inspiratory limb was 21 mg/liter. It fell to 19.2 mg/liter in 20 minutes, rising to 24 mg/liter after one hour of anesthesia and reaching 26 mg/liter (108% relative humidity at 25.5%) after 3 hours and 40 minutes.

The relationship between flow through the canister 14 and pressure in tube 12 is shown in FIG. 2 with the bypass valve 55 closed. Pressure varies from 40 to torr for variations in flow from ml/min. to 10 liter/- min. The relationship is linear for flow ranges of 1 liter/min (58 torr) to 10 liter/min (90 torr). The manometer on the line 12 was, therefore, calibrated in liters per minute in view of this relationship.

In the standard adult model patient experiment CO 200 ml/min. V, 600 ml. n=12) humidity in the tube 32 at the Y piece (FIG. 3) was 15 mg H O/Iiter at the onset (76% relative humidity at 23C). Humidity fell to 13.6 mg H Olliter (69% relative humidity at 23C) after 30 minutes, and then gradually rose and stabilized itself at 23 mg/liter after 3 hours and 20 minutes (116% relative humidity at 23C).

In the large adult model patient experiment (V CO, 300 ml/min. V, 600 ml), humidity followed very closely the pattern seen in the standard adult experiment. It was, generally speaking, approximately 1 mg H O/Iiter higher than in that experiment, but at stabilization it reached the same value. However, the drop in humidity, seen at the onset of the standard experiment, was not found.

In the pediatric model patient experiment CO 100 ml/min. V, 200 ml. n=20) the original humidity was higher (17 mg H O/liter or 86% relative humidity at 23C). Humidity dropped to 15 mg H Olliter (76% at 23) and then gradually rose and stabilized itself at 19.4 mg H O after three and a half hours (98% at 23C).

When attempts were made to control inspired moisture at 60% at ambient temperature (12.95 to 14.4 mg H O/liter at 22 to 26C), humidity in the inspiratory tube 34 remained within the range of 13.8 i 0.85 mg H O/liter over a 5 hour period.

There were no traces of carbon dioxide in the inspiratory tube 32 after 5 hours of use with large adult settings.

Pressures in the inspiratory and expiratory tubes 32, 36 were 4/21 cm H 0 and 4/18 cm H O during the clinical study and 4/32 and 4/28 cm H O during the laboratory or model patient studies, irrespective of the presence or absence of the canister 14 in the canister 22.

The humidity of anesthetic gases measured in the inspiratory tube 32 at the Y piece during the clinical study was very close to that predicted by laboratory tests. All errors noted were slightly in excess of expected humidity.

The temperature of the water in the vaporizer canister 14 was generally higher than gas temperature by a few degrees centigrade except during the early period of vaporization when the reverse obtained. In all cases, Y-connection temperature reached water temperature after 3 hours. In no instance did any of these temperatures rise above 29C. Room temperature for all experiments was maintained at 23 i 0.7C.

FIG. 3 shows the results of humidity in the inspiratory tube 32 at the Y-connection, in mg/liter, using an anesthetic gas input through anesthesia machine 10 of 5 liter/min. Curve 66 represents the results for a standard adult (\7 co 200 ml/min.; V, 600 ml. and n=12);

curve 68 represents the results for a large adult CO 300 ml/min.; V, 600 ml and n=12); and curve 70 represents the results for a pediatric patient CO 100 ml/min.; V, 200 ml and n=2()).

The humidity in the inspiratory tube 32 at the Y connection 34 is the moisture derived from the mixture of two gas streams; that from the canister 14 which delivers moist gas to the inlet port of the inspiratory dome valve 28, and gas exhaled by the patient after passage through the reactive granules of the canister 22. As time progresses, the reaction of neutralization by carbon dioxide warms both the reactive granules and the water in the canister 14 and synthesizes water, thus raising the humidity of both gas streams. The transient initial fall in temperature and humidity in the inspiratory gas stream for \7 CO 300 ml/liter is due to cooling of water in the canister 14 caused by the latent heat of vaporization before enough heat is generated by the reaction of neutralization. A larger C (300 ml/min.) produces sufficient initial heat to mask this effect.

If the bypass valve 55 is fully opened, humidity in the inspiratory tube 32 is derived from moisture and heat evolved from the patients breath; from heat and moisture generated by the reaction of neutralization of the reactive granules in the canister 22, and from water incorporated in the granules by the manufacturer (15% weight for weight for the combination of barium hydroxide-lime USP). Humidity can then be predicted and controlled by adjustments in dry anesthetic inputs and by appropriately selecting ventilatory settings, i.e., CO V,, thus eliminating the need for using sensors in the system such as those shown at 59, 62 and 56. If the bypass valve is fully closed, the dilutional effect of fresh dry gases arriving at the inspiratory dome valve from the anesthesia machine is lost, and humidity is only dependent on carbon dioxide inflow to the inspirational dome valve 28, room temperature, and duration of use (see FIG: 3). If the bypass valve 55 is partially opened, inspired humidity depends on the relative mixture of humidified gases coming from the canister 22 and the canister 14, and on the fraction of fresh gas inflow (dry) which bypasses the canister 14. In estimating the final humidity a correction should be introduced for loss of moisture caused by condensation in the collecting line proximate the bypass valve 55 and in the channels between the canister 22 and inspiratory dome valve 28.

When it is desired to control inspired humidity for experimental reasons, with a thermometer and hygrosensor in the inspiratory limb at the Y piece, it is necessary at the onset of the experiment to dilute the original high humidity by adjustments of the bypass valve 55. When the bypass valve is fully opened and humidity still rises above the required value, it can be further controlled by increasing the fresh gas input through anesthesia machine 10.

Modifications in and to the above described preferred embodiments may be made by those skilled in the art. It is intended to cover all such modifications which fall within the spirit and scope of the invention as defined in the claims appended hereto.

What is claimed is:

1. In an anesthesia delivery system for a patient said system having a firstcanister with a gas diffusion stone and water contained therein for humidifying anesthetic laden gas to be fed to the patient, means for feeding anesthetic laden gas to said first canister via said diffusion stone, said water covering at least part of said gas diffusion stone whereby said dry anesthetic laden gas becomes humidified upon passage through said water, said anesthetic laden gas passing through said diffusion stone and said water, and means for removing humidified, anesthetic laden gas from said first canister and feeding it to said patient, the improvement comprising: a second canister surrounding said first canister, reactive material means in said second canister for reacting with carbon dioxide laden gases in an exothermic reaction, said reactive material means at least partly surrounding said first canister, means for feeding said carbon dioxide laden gases to said second canister whereby the reaction of carbon dioxide with said reactive material means liberates heat which heats the water in said first canister for humidifying the anesthetic laden gas passing through the water in said first canister.

2. The anesthesia delivery system according to claim 1 wherein said reactive material is a material selected from the group consisting of oxides and hydroxides of alkaline earth metals and alkaline metals, guanidine, substituted guanidine in which the pK valve is more than 10, strongly basic anion exchange resins which retain their positive charge up to pH 12, and mixtures of the foregoing.

3. The anesthesia delivery system according to claim 1 wherein said reactive material is a material selected from the group consisting of the oxide or hydroxide of barium, calcium and lithium and mixtures thereof.

4. The system according to claim 2 wherein said resins are taken from the class consisting of diethanol amino ethyl cellulose, epichlorhydrin triethanolamine cellulose, DEAE dextran, polyethyleneimine cellulose and triethylaminoethyl cellulose.

5. The anesthesia delivery system according to claim 1 wherein said reactive material is a mixture of barium hydroxide and lime of USP grade.

6. The anesthesia delivery system according to claim 1 further comprising an inspiration tube and an expiration tube connected to a patient, said expiration tube being connected to said second canister for conveying carbon dioxide laden gases from said patient to said second canister for reaction with said reactive material.

7. The anesthesia delivery system according to claim 6 further comprising bypass valve means fluidly connecting said means for feeding anesthetic laden gas into said first container and said means for removing anesthetic laden gas from said first container, said bypass means being normally closed to prevent said fluid communication and being openable to permit fluid communication to take place to reduce humidity in the said inspiration tube.

8. The anesthesia delivery system according to claim 1 further comprising means for removing gases having reduced amounts of carbon dioxide from said second canister, means for mixing the removed gases with humidified gas containing an anesthetic, and means for delivering the humidified, anesthetic laden gas to the patient.

9. The anesthesia delivery system according to claim 1 further comprising means for mixing dry anesthetic gas with the gas in said inspiration tube.

10. An anesthesia delivery system comprising a first canister anda second canister surrounding said first canister, said first canister having water and a gas diffusion stone therein, means for feeding dry anesthetic laden gas into said first canister via said gas diffusion stone, said water covering at least part of said gas diffusion stone whereby said dry anesthetic laden gas becomes humidified upon passage through said water, and means for removing the humidified anesthetic laden gas from said first canister; said second canister containing a reactive material means for exothermically reacting with carbon dioxide in a heat liberating reaction, said reactive material at least partly surrounding said first canister; an inspiration tube and an expiration tube for use by a patient, said expiration tube being in fluid communication with said material means whereby at least some of the carbon dioxide in the expirated gas reacts with said reactive material means to release heat to heat the water in said first canister, said reactive material also removing at least some of the carbon dioxide from said expirated gas; means for removing the gas having reduced carbon dioxide content from said second canister and means for mixing said gas having reduced carbon dioxide content with said anesthetic laden gas removed from said first canister, said mixing means being in fluid communication with said inspiration tube.

11. The anesthesia delivery system according to claim 10 wherein said reactive material means is a material selected from the group consisting of the oxides or hydroxides of alkaline earth metals and alkaline metals and mixtures thereof.

12. The anesthesia delivery system according to claim 10 wherein said reactive material means is a material selected from the group consisting of the oxides or hydroxides of barium, calcium and lithium and mixtures thereof.

13. The anesthesia delivery system according to claim 1 wherein said reactive material means is a mixture of barium hydroxide and lime of USP grade. 

1. In an anesthesia delivery system for a patient said system having a first canister with a gas diffusion stone and water contained therein for humidifying anesthetic laden gas to be fed to the patient, means for feeding anesthetic laden gas to said first canister via said diffusion stone, said water covering at least part of said gas diffusion stone whereby said dry anesthetic laden gas becomes humidified upon passage through said water, said anesthetic laden gas passing through said diffusion stone and said water, and means for removing humidified, anesthetic laden gas from said first canister and feeding it to said patient, the improvement comprising: a second canister surrounding said first canister, reactive material means in said second canister for reacting with carbon dioxide laden gases in an exothermic reaction, said reactive material means at least partly surrounding said first canister, means for feeding said carbon dioxide laden gases to said second canister whereby the reaction of carbon dioxide with said reactive material means liberates heat which heats the water in said first canister for humidifying the anesthetic laden gas passing through the water in said first canister.
 2. The anesthesia delivery system according to claim 1 wherein said reactive material is a material selected from the group consisting of oxides and hydroxides of alkaline earth metals and alkaline metals, guanidine, substituted guanidine in which the pK valve is more than 10, strongly basic anion exchange resins which retain their positive charge up to pH 12, and mixtures of the foregoing.
 3. The anesthesia delivery system according to claim 1 wherein said reactive material is a material selected frOm the group consisting of the oxide or hydroxide of barium, calcium and lithium and mixtures thereof.
 4. The system according to claim 2 wherein said resins are taken from the class consisting of diethanol amino ethyl cellulose, epichlorhydrin triethanolamine cellulose, DEAE dextran, polyethyleneimine cellulose and triethylaminoethyl cellulose.
 5. The anesthesia delivery system according to claim 1 wherein said reactive material is a mixture of barium hydroxide and lime of USP grade.
 6. The anesthesia delivery system according to claim 1 further comprising an inspiration tube and an expiration tube connected to a patient, said expiration tube being connected to said second canister for conveying carbon dioxide laden gases from said patient to said second canister for reaction with said reactive material.
 7. The anesthesia delivery system according to claim 6 further comprising bypass valve means fluidly connecting said means for feeding anesthetic laden gas into said first container and said means for removing anesthetic laden gas from said first container, said bypass means being normally closed to prevent said fluid communication and being openable to permit fluid communication to take place to reduce humidity in the said inspiration tube.
 8. The anesthesia delivery system according to claim 1 further comprising means for removing gases having reduced amounts of carbon dioxide from said second canister, means for mixing the removed gases with humidified gas containing an anesthetic, and means for delivering the humidified, anesthetic laden gas to the patient.
 9. The anesthesia delivery system according to claim 1 further comprising means for mixing dry anesthetic gas with the gas in said inspiration tube.
 10. An anesthesia delivery system comprising a first canister and a second canister surrounding said first canister, said first canister having water and a gas diffusion stone therein, means for feeding dry anesthetic laden gas into said first canister via said gas diffusion stone, said water covering at least part of said gas diffusion stone whereby said dry anesthetic laden gas becomes humidified upon passage through said water, and means for removing the humidified anesthetic laden gas from said first canister; said second canister containing a reactive material means for exothermically reacting with carbon dioxide in a heat liberating reaction, said reactive material at least partly surrounding said first canister; an inspiration tube and an expiration tube for use by a patient, said expiration tube being in fluid communication with said material means whereby at least some of the carbon dioxide in the expirated gas reacts with said reactive material means to release heat to heat the water in said first canister, said reactive material also removing at least some of the carbon dioxide from said expirated gas; means for removing the gas having reduced carbon dioxide content from said second canister and means for mixing said gas having reduced carbon dioxide content with said anesthetic laden gas removed from said first canister, said mixing means being in fluid communication with said inspiration tube.
 11. The anesthesia delivery system according to claim 10 wherein said reactive material means is a material selected from the group consisting of the oxides or hydroxides of alkaline earth metals and alkaline metals and mixtures thereof.
 12. The anesthesia delivery system according to claim 10 wherein said reactive material means is a material selected from the group consisting of the oxides or hydroxides of barium, calcium and lithium and mixtures thereof.
 13. The anesthesia delivery system according to claim 1 wherein said reactive material means is a mixture of barium hydroxide and lime of USP grade. 